1. Technical Field
The present invention relates to a wireless key system to perform wireless communication between a main body communication device mounted in a main body, such as a vehicle or a house, and a movable wireless key.
2. Description of the Related Art
There is a known wireless key system that automatically locks/unlocks a vehicle door when a wireless key (electronic key) carried by a user who moves approaches a communication device mounted at the vehicle door (see Patent literature 1). In such a wireless key system for vehicles, wireless communication is performed between the communication device and the wireless key when the wireless key enters an area around the communication device and, at the same time, a signal containing an identification code (ID code) transmitted from the wireless key is received by the communication device through wireless communication. The communication device compares the identification code of the wireless key contained in the received signal with an identification code stored in a memory of the communication device. Upon determining that the identification codes coincide with each other as the result of the comparison, locking or unlocking of the vehicle door is allowed.
In such a wireless key system for vehicles, a low frequency (LF) radio wave is generally used for communication from the vehicle side communication device to the wireless key, and an ultra high frequency (UHF) radio wave is generally used for communication from the wireless key to the vehicle side communication device. In addition, there is provided a long wave receiving antenna on the wireless key side which is formed of a three axes antenna having directivities in X-axis, Y-axis and Z-axis in view of the directivity of an antenna.
Also, in such a wireless key system for vehicles, transmitting antennas are mounted inside and outside the vehicle and the wireless key has a function to measure intensities of received signals. The function to measure intensities of received signals is as follows. It is determined whether the wireless key is located inside or outside the vehicle based on signal intensities obtained through the three axes antenna, respectively, from a wireless signal transmitted from the vehicle side communication device through a plurality of transmitting antennas and the determination result is transmitted to the vehicle side communication device using a wireless signal. In addition, the vehicle side communication device has a function to perform operations that the vehicle door is automatically locked upon determining, for example, that the wireless key is moved out of the vehicle according to the wireless signal of the determination result, or the vehicle door is automatically unlocked when the wireless key approaches the vehicle.
Patent literature 1: Japanese Patent Kokai No. 2008-115648